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Microbiologists examine potential of nano-wires
BY ANDREW VOWLES
Guelph microbiologists are studying a novel method used by bacteria to “breathe” heavy metals in rocks that may ultimately help scientists harness microbes for cleaning up toxic environmental waste.
Prof. Terry Beveridge, Molecular and Cellular Biology, says that, besides their potential eco-scrubbing function, rarely seen bacterial structures called nano-wires may also allow bacteria to carry out a kind of primitive “schmoozing” by connecting large numbers of cells.
The Guelph researchers and their collaborators at the Pacific Northwest National Laboratory (PNNL) in Richland, Wash., have submitted a paper about their findings to the Proceedings of the National Academy of Sciences for review.
Their paper describes how minuscule protein filaments that grow from bacterial cell walls appear to enable microbes living in oxygen-free environments deep underground to snag iron from minerals such as hematite or magnetite in much the same way we use oxygen.
“They are literally breathing the solid rock,” says Beveridge.
Their data suggest that these nano-wires conduct electrons into the nearby mineral, effectively acting as live wires to short-circuit the electrons into the rock and turn the iron into a “breathable” form.
Earlier this year, he completed two weeks of experiments on the bacteria in his science complex lab, along with Dianne Moyles, a U of G technician, and PNNL microbiologists Yuri Gorby and Catherine Reardon.
“This is very exciting,” says Beveridge, who holds the Canada Research Chair in the Structure, Physical Nature and Geobiology of Prokaryotes. “We were jumping up and down.”
Studying this novel process may help the scientists learn more about using bacteria to immobilize toxic environmental metals and radioactive contaminants such as plutonium and uranium, he says.
His current project is funded by the U.S. Department of Energy (DOE) under a special Grand Challenge program. This funding program supports two research networks across North America studying large-scale aspects of biogeochemistry and membrane biology. The projects are intended to help DOE clean up toxic heavy metals and radioactive waste from the environment.
Under the Biogeochemistry Grand Challenge, Beveridge and his U of G lab team are receiving $100,000 a year for three years, beginning in fall 2004. (The only Canadian member of the network, he also served on the committee planning the Grand Challenge funding.)
This research network, led by PNNL scientists, is studying how organisms exchange energy and electron flux with minerals in soils and sediments and below the Earth's surface.
Beveridge and his collaborators study Shewanella bacteria for possible use in cleaning up DOE-contaminated sites. The PNNL's Gorby coined the term “nano-wires” to describe these bacterial filaments that appear to be involved in metal reduction, although researchers at the University of Massachusetts were the first scientists to publish on the phenomenon.
Continuing their recent work here at Guelph, Beveridge and Moyles are now culturing the micro-organism to learn more about conditions that encourage bacteria to make these nano-wires and to better understand how these filaments work.
They use innovative electron microscopy techniques to view these delicate structures — only a few nanometres thick — and to establish their use in the biocycling of iron, an essential nutrient. Because micro-organisms play an important role in the global cycling of many elements — carbon, oxygen, nitrogen, phosphorus and essential metals — studying nano-wires may also help in understanding all such processes, which Beveridge calls key to sustaining the environment and life.
“Even though they're minute cells and the tiniest life forms, they have a tremendously huge impact on the global cycling of elements,” he says. “Microbes have learned to deal with the most toxic substances we can think of, whether natural or human-made, whether organic or inorganic.”
Apart from their iron-respiring role, these nano-wires may also turn out to be important in bacterial communication, he says.
“They could be a primitive ‘neural network' that's been around since the dawn of life billions of years ago. It's possible that microbial cross-talk was going on well before Alexander Graham Bell invented the telephone.”
